In systems producing large amounts of waste heat as a by-product of a necessary process, a method for efficiently removing such waste heat is highly desirable. This need is particularly acute for space systems wherein large amounts of heat are generated as a by product of space system operation. The weight limitation accompanying space designs dictates an efficient device for eliminating waste heat.
Numerous advanced heat radiation concepts have been proposed as potential improvements for heat rejection. U.S. Pat. No. 4,603,732, entitled "Heat Management System for Spacecraft" to Niggemann, et al, discloses a two phase heat management system which dissipates heat by evaporating a liquid and rejects heat by condensing the vapors. U.S. Pat. No. 4,572,285, entitled "Magnetically Focused Liquid Drop Radiator", to Botts, et al, discloses a magnetically focused liquid drop radiator for application in rejecting energy from a spacecraft, using magnetizable droplets.
U.S. Pat. No. 3,161,593, entitled "Method and Apparatus for Utilizing the Formation of Energy of Petroleum Deposits", U.S. Pat. No. 3,856,483, entitled "Method and Device for Degassing Liquids", U.S. Pat. No. 3,996,027, entitled "Swirling Flow Bubble Trap", U.S. Pat. No. 3,151,961, entitled "Vortex-Type De-Aerator and Strainer", U.S. Pat. No. 2,634,907, entitled "Process and Apparatus for Centrifugial Deaeration", U.S. Pat. No. 2,592,680, entitled "Apparatus for Removal of Gasses from Liquids", U.S. Pat. No. 2,216,939, entitled "Rotary Gas and Oil Separator", U.S. Pat. No. 3,271,929, entitled "Vortex Type Reconditioner and Reconditioning Method for Used Drilling Mud", U.S. Pat. No. 3,290,864, entitled "Gas Separation Pump for Liquid Circulating Systems", U.S. Pat. No. 3,771,290, entitled "Vortex De-Aerator" , and U.S. Pat. No. 3,797,661, entitled "Method and Apparatus for Separating Granules from a Liquid" all disclose various forms of liquid separation from another medium. U.S. Pat. No. 3,405,454, entitled "Waste Management System" discloses a human waste treatment system. In the present application, however, liquid collection is performed in the vacuum of space, and the liquid is collected rather than separated from another medium.
Even under the most extreme of circumstances, the above disclosures have a low utility as applied to the space environment. In addition to satisfying the generalized requirements of space power systems, the radiator must avoid single-point failure modes; interface with the relatively high temperatures of the power conversion system; have compact stow capability; and offer a significant decrease in total system mass, while operating in a hostile environment.
Current systems for heat rejection in space rely primarily on the proven heat pipe radiator. Evolutionary improvements in heat pipe radiators should increase survivability and provide compact stow capability. Design improvements to enhance heat transfer and condensate flow should decrease radiator specific weight and extend the operating regime to higher heat fluxes. However, these potential improvements are limited when both survivability and decreased system weight goals are prescribed. In addition, heat pipe concerns include (1) susceptibility to directed energy, including effects of heat transfer fluid loss, (2) noncondensible gas formation over the 10-year life, and (3) total system mass of large-scale systems, especially when provided with protection barriers; as are required for hostile threats.
Another heat transfer scheme involves the transmission of heat to a fluid medium, the exposure of the fluid to the vacuum of space, and the subsequent collection of the heat depleted fluid for recycling back through the system. Typically, droplets of a heat-transfer fluid (e.g., silicone oils, liquid metals) would be ejected from barely visible holes approximately 25 to 100 microns in diameter at velocities of 5 to 20 meters/second. These small holes provide the thin streams which then break up into small droplets approximately twice the diameter of the orifices. For large space systems requiring the rejection of from 5 to 20 megawats thermal, hundreds of thousands to millions of orifices would be required. This poses an especially difficult cost challenge, and the orifices must all be accurately formed and maintained to avoid misdirected droplet streams. The radiating area for this amount of heat would be approximately half the size of a football field. Droplets would be ejected towards the collector over distances of 10-50 meters. During their several seconds of flight, they would radiate energy to space.
At the end of their path, they would strike a centrifugal collector, spin to the outer rim of the collector, and form a thick annular film which would be pumped through a pitot tube into a higher pressure pump. The higher pressure pump would then send the liquid back into the power-conversion system. The reheated liquid would then be ejected through the orifices again to cool and recirculate. In order to place such a droplet forming and collection system in the harsh environs of space an immediately recognizable series of problems must be solved.
The collection and pumping of liquids in a microgravity environment presents major problems. An ordinary centrifugal collector can provide moderately high collecting and pumping forces, but those which use rotary seals with flow introduced through an axial pipe, may cause the rotary seals to leak, and the additional flow introduced decreases the net outlet flow. These devices, which were developed by the University of Washington and Spectra Technology, Inc., nevertheless demonstrated successful operation. Other types of centrifugal collectors, using an auxiliary air flow to collect urine, have also been developed and flown on Skylab. A similar device has been flown on the Space Shuttle.
In addition, such a system for heating the fluid, transmitting the fluid through space to allow radiation and capturing the fluid for recycling, must capture high temperature liquid metals and lose less than one part per one hundred million of the fluid medium in order to meet the long term requirements of that system.
A typical centrifugal collector/pump design having a rotating collector, pitot tubes for low pressure of outflow of collected liquid, and separate, higher pressure pumps for reaching the pressures required at the droplet generators will not solve the following problems:
(a) The collector has a very low velocity on the inner surface near the rotational axis (and zero velocity on the rotational axis). Therefore, droplets striking this region may not acquire sufficient velocity to be forced to the outer rim. Droplet loss could occur in this region.
(b) The motor, gearbox, collector, pump, and pitot tubes are all separate entities "bolted" together. Multiple interfaces, housings, flanges, etc., increase weight and volume. An integrated system will reduce weight and volume.
(c) The motor, collector, and pump must be mounted by a less efficient structure that attaches to the rear of the collector, and then the return line must be run along with the structure.